MCBG Session 13 - Gene Expression Flashcards
What is the central dogma of biology?
What are the 2 processes in this dogma called?
Where do these processes occur within the cell?
DNA –> RNA –> Protein
DNA –> RNA = Transcription (reading the code)
RNA –> Protein = Translation (code transformed)
Transcription = nucleus. Translation = cytoplasm (RER)
What are the 3 regions on DNA involved in transcription?
What terminology is used for directions of these regions?
1) Promoter region (where initation of transcription occurs)
2) Coding region - region where code is copied
3) Terminator region (where termination of transcription occurs)
Upstream & Downstream - e.g.: coding region is always upstream of promoter region.
Does a gene code for 1 protein, 1 polypeptide or 1 functional unit? Explain why.
- Doesn’t code for just one protein, a gene can code for multiple proteins, e.g.: Hb has 2 genes.
- Doesn’t code for just one polypeptide, as not all genes are expressed as polypeptides and not all RNA molecules are translated.
- 1 gene does code for 1 functional unit - either a sequence of AA’s in a polypeptide or a sequence of nucleotides in untranslated RNA.
What are the main differences between DNA and RNA.
1) RNA has hydroxyl group of C2 (DNA has H removed)
2) RNA contains uracil (U) instead of thymine (T)
3) RNA molecule are single stranded (DNA is double)
4) RNA can form stem loops and other complex 3D structures with non-standard base pairings.
How much of total RNA does rRNA make up?
How many kinds and copies or rRNA are there?
How well conserved is rRNA?
- 80% of total RNA
- Few kinds, but many copies of rRNA
- Very well/highly conserved
How much of total RNA does tRNA make up?
How many kinds and copies of tRNA are there?
What is each tRNA dedicated to?
- 15% of total RNA
- Roughly 100 kinds, many copies (generally small)
- Each tRNA is dedicated (cognate) to one of the 20 AA’s
How much of total RNA does mRNA make up?
How many kinds and copies of mRNA are there?
- 2-5% of RNA
- 100,000’s of kinds, very few copies
NB: there are many other types of RNA, e.g.: SiRNA which have important functions within the cell.
What are the 3 things a cell requires for transcription to occur and what are the 3 stages?
1) A template - DNA code
2) An enzyme - RNA polymerase
3) Substrates - NTP’s (nucleotide triphosphates)
Initation –> Elongation –> Termination
What drives the reaction of transcription?
What direction does synthesis of RNA occur in?
- Hydrolysis of PPi by pyrophosphates
- Synthesis from 5’ to 3’
Which RNA polymerase enzymes synthesis rRNA, mRNA and tRNA?
rRNA = RNA polymerase 1 mRNA = RNA polymerase 2 tRNA = RNA polymerase 3
Which subunit on RNA polymerase is required for specific DNA binding on promoter?
Sigma subunit - makes RNA specific, otherwise would be made at random.
What occurs during initiation of transcription?
- Transcription factor (TF) binds to promoter region
- Specifically to TATA box (specific sequence recognised by TF’s)
- More TF’s bind to sequences upstream of TATA
- RNA polymerase is recruited
What occurs during elongation of transcrption?
- DNA helix unwound into single strand
- Formation of transcription bubble (17bp)
- Template strand read 3’ to 5’, RNA synthesis occurs 5’ to 3’
- As transcription bubble advances, DNA helix reforms behind it
What is the transcribed and non-transcribed strand of DNA in transcription called?
Non-transcribed = coding strand Transcribed = template strand
Transcription termination is sequence-dependent, what does this result in the production of?
What is required to produce the mature version?
- Primary RNA
- RNA processing needed to produce mature RNA
